Telegraph repeater



Jan- 9, 1940- G. s. vl-:RNAM 2,186,741

TELEGRAPH REPEATER Filed 0G13. 27, 1937 3 Sheets-Sheet l lllll @Mum fwnvIvIV ATTORNEY Jan. 9, 1940. Q s VERNAM 2,186,741

TELEGRAPH REPEATER Filed oct.' 27, 1937 s sheets-sheet 2 s KLJ@ INVENTORG/LBERT 5. VER/YAM ATTORNEY Jan. 9, 1940. G. s. vERNAM TELEGRAPHREPEATER 3i Sheets-Sheet 3 Filed Oct. 27, 1937 Patented Jan. 9, 1940 y2,186,741 y y i l TELEGRAPH REPEATER y y `.Gilbert S. Vernam,HackensackQN. J., assigner to Postal 'lelegraph-Cablef Company (NewYork), New York, N.' Y., a corporation of New York Application october,2r,

'13* Claims.y (Cl. 1785-71) e My invention relates to improvements intelegraph repeaters and particularly to single line or simplexrepeaters. l

One objectief my invention is toy design a telegraph `repeater systemthat will operate athigh .speed and will accurately repeat signals, ineither direction, between two single line or loop circuits.

Another object of my invention is to provide a y'repeater circuit withany vassocia-ted switching.

means for cutting the repeater circuit and closingthe line vvcircuitthrough the associated'relay `winding on'- each side of the repeater,independent oitherepeating contacts of. theother relays, thus stoppingthe lrepeating of signals 4in both directions.`

It is a further'object of myinvention toestablish a. local test circuitthrough the repeating.

`contacts of both relays atthe time thatthe repeater circuitA is cut. lIt is a further object of my invention to'provide a `repeater for singleline operation in which relay locking circuits entirely separate from`the line orloop circuit are provided and used with a relay havingseparate pairs of make and break' contacts v arranged so that thecontacts 4may be adjusted to operate as make-before-break contacts.-

Itv is affurther object of my invention Vto prol .vide-sounder'circuitscombined with'the separate relay lockingcircuits so arranged that'thesounder` current decreases and the locking current vfor -eachrelayincreases upon the-closure of back f contacts of the other relay.`.3 l

vIt isa'further object of my inventiony to providea switchingarrangement for separating the sounder and ylocking circuits'anddisabling the locking circuit of each line relay upon the cutting ofthe repeater circuit.

both polarized. signals. for printer motor control `or for. operatingcall indicating signals, e and maille-break signals for regular f'communication. Otherobjectsand features of the' inventionv wiil bepresented in the particular vdescription ci my invention made withrespect to the ac-v companying drawings, in which:

Fig. yl `discloses a schematic lcircuit of one form l oiV repeater inaccordance with my invention,

1937,-.seria1Na 171,205

fOFFICE Fig. Zoillustrate's by way of example a -socalled v half-set.repeater: connection for use with the repeater illustratedinvFig. 1.

Fig. 3 is a schematic .circuit of another embodiment of arepeater` inaccordance with'my i;

invention, andl i. 1

. Fig. 4 illustrates an application of the repeaterv shownV in Fig. 3 toagcall.signallingprinter arrangement. y f v Referring more particularlytothe" drawings,

in Fig. 1.r'eferencenumeral II represents a station connected by line I2through a repeater to line I3, and the telegraph stationfapparatus des-`ignated generally as I4. The switches and relay [..contacts- 'of therepeater circuit are shown in their normal position which theyA assumewhen the repeater isy connected to aline and no Signals f are beingtransmitted. Thus, the line I2'is connected through the line relaywinding I5 of line yrelay Iii-contact 2 oiA switch element 22 of twoposition switch 3 which comprises the switch elev,ments n Ila-24.inclusive, the front contact oflne `relayf3I',contact 2 of switchelement 2l, to positive battery 33. Line I3 is connected through.contact 2 of switch element 'I2 of two position switch lil, linewinding-2l of line relay 3| through contact 2 of switch elements 'II and'lli` of switch 4, contact-2 of vswitch element 20, the front contact ofrelayrIE, contact 2-.of switch element I5, e

.Contact 2 of switch; element `69 of switch 4 to battery at 28. Upon therelease and operation .of transmitting key I'I, for example, the line.circuit through the linewinding of relay I6 is 4opened*v and closed.-`Relay VI6 willA respond rto vthese signals, opening and closing thelinecircuit breaking of -this latter line circuit, however, a holdingcircuit is -established for line `relay `3l from ground-through theholding winding 30 of line relay 3|, contact`2 of switch element I1`contact 2 of switch element I8, through resistance 35 to battery 25, sothat relay. 3|?y remains 35 through thefline winding of relay 3l; `Upon,4o of switch 3, the back Contact of line relay I6,

energized andthe line circuit connected to trans-j mission line I2 isnot broken at theiront contact `of.relay 3|.A g

Similarly, when signals are being transmitted from I4, relay-3lreleases, and the opening of its 4iront contactsopens the circuitofline,l2 andl 1 a holding circuit pis established through the backcontacts of--relay 3l and contact of switch elen'ientv 24 to establish aholding current through the auxiliary relay `winding 34 oi-.relay IIS'.-The contacts controlled by earl of the line relays vIt and 3l are madeiiesik-i and are adjusted so that when the relay releases, the backcontacts close before the front contacts open, and when the relayoperates the front contacts close before the back contacts open, so asto produce a makebefore-break action and maintain the other line relayenergized, so that signals may be repeated by one relay from one stationto the other, without efecting the Iother relay.- The line relays withseparate contacts arranged for make-before-break operation permit theuse of the repeater for repeating between two two-wire loop circuits, orreceived over either wire of either loop, thus 'permitting the repeater`to be -connected in series with loops of .other repeaters .to

form a 3-way repeater as is well .known in the4 art. This arrangementalso permits the Sounders to be operated in a local circuit at therepeater to avoid adding the inductance of the sounder winding in theline or loop circuit.

The operation of the sounder circuit will now be explained. With bothline relays operated, as shown in Fig. 1, a circuit exists through thesounder 35, extending from battery through the resistance 36, resistance31, the winding of sounder 35 to ground. Simultaneously a parallelcircuit exists from contacts 2 of switch elementV I8 of switch 3,resistance 38, and the auxiliary winding of line relay 3I to ground.This circuit is arranged with the resistance of the various elements sochosen that the current through the relay winding 30 under these normalconditions is insuiiicient to operate relay 30, but the current rthroughthe sounder is sufcient to operate the sounder. A similar circuit may betraced for sounder 39 from battery 25, through resistance 4D associatedwith element 23 of swtch 3, sounder 33 to ground, and also in paralleltherewith through the auxiliary locking winding 34 of relay I 6 inparallel therewith. The current through the locking winding of each ofthe line relays serves as a biasing current, the springs associated withthe armature and relay contacts being strong enough to overcome thisbiasing current unless the armature is held by a current in the loopcircuit. This biasing currentincreases the permeability of the magneticcircuit and makes the operation of the relays more sensitive.

' When one of the line relays, for example relay I6, releases, its backcontacts create a short circuit around resistance 38, so that thelocking winding 33 of relay 3| is shunted directly across the sounderand its resistance 31. The sounder current therefore decreases,releasing the sounder, and the relay locking current'increases to avalue suiiicient to hold relay 3l operated in spite of the fact that theline circuit is now open at the front contact of relay I S. Accordingly,the repeater will operate to repeat the signals as explained above, andsimultaneously each sounder will respond to the signals repeated by thecorresponding relays. Thus, these Sounders may be used for monitoringthe signals at the repeaters. Although, as described above, ordinaryMorse telegraph keys and Sounders have been shown, it is clear that therepeater circuits may be used for other types of telegraph apparatus,lforl example, telegraph printers or teletype printers.

It can vbe seen that with the repeater such as described, if troubleconditions should cause either line to go open, the other repeater willalso `open its circuit. The quickest method of locating the trouble isto operate a cut -or breaking circuit so that each of the loops throughthe line relays may operate independently of the other. This will `closethe loop that is not in trouble and will permit service over that partof the circuit, until the trouble is cleared.

In order to provide for such a cutting of the circuit, it is onlynecessary to operate switch 3 so that switch elements I1 to 24,inclusive, are each resting on contact I. This cut circuit may also beused whenever it is desired to prevent the repeater .from repeatingsignals from one loop to the other, as for example, to shutoff acustomers station while his circuit is being lined up. It may also beused for checking the adjustment of the various relays.

The operation of the switch 3 to position I, removes the front contactsof relay 3I from the line circuit I2 and closesthe line through contactI of switch element `2 I directly to battery 33, and similarly itremoves the contacts of relay I 6 from line I3 and closes line I3through contact I of switch element I9 to battery 28, permittingcommunication over these independent loop circuits withoutrepeatingsignals from either loop to the other. At the same time theshut releasing circuits oi Sounders 35 and 39 are closed through 'therelay back contacts directly to ground, and the biasing circuits throughthe auxiliary windings of relays I5 and 3l are separately energizedthrough contact -I of switch elements 23 and I8, respectively.Accordingly, the signals from II and I4 may be independently received atthe relay station over line relays I6 Aand 3I operating substanl tiallyin the same way as previously described to energize Sounders 35 and 39.Simultaneously a test circuit is produced from battery 25 through testjack 4I, front contact of relay IB, Contact I of switch element 2B,front contact of relay 3I and contact I of switch element 22 to ground,permitting a test to be made of the relay contacts to determine anyfaults that may einst therein. By inserting a plug connected to amilliammeter in jack 4I the output signals of either relay may betested, and the relays may be conveniently adjusted to repeat unbiasedsignals. I

It is sometimes desirable to connect a single line repeater to thesending and receiving legs of a duplex terminal set so that signalsbeing 'transmitted in either direction over a duplex line may betransmitted or received through the repeater to or from a single Wireline or a single loop circuit. When used in such a connection, therepeater is termed a half-set repeater, and it provides means forfurnishing single or halfduplex operation over a duplexed line. Inaccordance with my invention provisions are made for switching theconnections of the repeater illustrated in Fig. 1 to operate as ahalf-set. To convert the repeater illustrated inl Fig. 1 for half--ciuplex operation, switch 4 is moved to the left position illustratedin Fig. 1, whereby switch 4 is arranged sothat its various switchingelements are on the number I contacts. Thus, connections arelestablished to each of the conductors 50, 5I, 52 and 53 of Fig. 1.

Fig. 2 illustrates the connection of these wires to the sending andreceiving legs of a duplex terminal set circuit for operation with therepeater in a half-duplex arrangement. With this arrangement, signalsfrom II are transmitted through the winding of relay I 6 in the samemanner as previously described. However, the sending device i4 and lineI3 are disconnected from the line winding of relay 3| by the movement ofthe switch element 12 from contact 2 to Contact I, and the circuit tothe line winding 21 of relay SI now extends from contact IOI- of duplexline relay H15 "(Fig. 2), through receiving leg conserve to make andbreak its front contactsfthus repeating the signals throughthe repeaterto receiver I I and simultaneously operating the receiving sounder 39 atthe repeater for vmonitoring purposes. a; i

For transmission of signals from II to the duplexv line, the batteryconnection of thefront contactsjof relay I6 is broken at contact 2 ofswitch element 69 an dis connected through'contact I, sendinglegconductor 50and the winding'of pole changer relay |06 topcsitivebattery at |01.,` This circuit then extends from battery |01 through thej circuit justvnamed, contact 2 of switch 'element lffrontcontacts ofvrelay I6, contact 2 of switch element 20, contact I of switch element 10and conductor 5I to ground at |08. Associated with relay |06 are twocontacts, front contact F being. associated. with a negative battery andback contact B being associated with a positive battery. Contact tongue|09 yisl connected through'a suitable conductor IIO vand inductance IIIt'o the midpoint of therelay winding of Arelay |05.

Accordingly, signals transmitted from II serve '35 to makeand break thesending leg` circuit at the iront contact of relay I6, thus causingalternate energizing and deenergizing of relay" |064 and operatingcontact tongue |09 to alternately apply positive and negative signalimpulsesto the line I 04 over the winding of relay |05. Since thesesignals are applied at the midpoint of relay winding vI 05, inaccordance with the well known methyod of duplex operation, they willhave equal and n opposite effects upon the two windingsof the vpolarrelay |05 and accordingly will not affect the contact IIiI. Since thesoundercircuit 'and the relay holding circuit are identical with thoseabove described, a repetition of the operation'of these circuits is notconsidered necessary at this point.

Fig. 3 accordancev with my invention. a conventional printer' circuit isillustrated as the main office printer at 30| enclosed in broken lines,arranged to be connected through a -jack discloses another forni ofrepeater in vof a switchboard 302, within the bro-ken line block andthroughv line 303, to 'the terminal 304 of the repeater. Incomingsignals from the printer are applied through a line jack and resistor,line 303, c0ntact'2 of switch element 304, front contacts of relay3I6,'contact il of switch element 306, the upper winding 3I'i of relay3I8, contact I of switch element 32|, the lower winding 323 of relay3I8, contact I of switch element y320, throughr'esistance 320 tonegative battery.

Another printer station 330, shown v'at the right of the figure enclosedby broken lines is connected over line 3.3i to terminal T332 of therepeater, and a circuit is established through contact 2 of switchelement 300, front contact of re-v In this figure,v

Thus incoming signals' switch element 306,` the back contact of relay3I8 and resistance 333' to ground at 340, preventing the front contactof relay 3I6.from opening.

Similarly, `when'signals transmitted from 330 the back contact of thisrelay closes, establishing a circuit from negative battery at 326through contact I of the switch element 320, winding 323 ofl relay SIB,contact I of switch element 32|, winding SI1 vof relayl 3I8," contact 2of switch element 335, back Contact of relay Sill, conductor 34|,Contact i of switch element 3I9, conductor 342,'resistance 343, to'ground at 340, thus establishing a holdingv circuit for relay 3I8, sothat it will not open its contacts. The contact springs of relays 3I6`and 3|8 are madeflexible and adjusted to make-before-break-so that theholding circuitsfor the respective relays ywill be maintained.

Contact switch elements 304 to 3|0, inclusive, are elementsof a singleswitch for two-position operation indicated generally at 345'and contactoperate to open 'the front contact of relay 3I6,

iii).

elements'3i9 to 32| are elements of the-three- 'position switchindicated generally at 346.

With switch 345 in the number two position as shown, and switch 346 inits number one position asv shown, the repeater operates as a straight,through repeater, similar to that illustrated in Fig. 1. -By throwing aswitch 345 to the right to establish circuits through the numberv onecontacts, a cutcircuit may be established for this re-` peaterg'so thatsignals incomingth'ereover will not be repeated tothe other line. Withthe switch thrown to this position signals incoming from 30| traversethe circuit `from terminal 304 through Contact I of switch element 365,'winding 3I1 of relay 3m, contact I of switch element 32|, lower winding323 of relay 3I8, contact I of switch element 320 and resistance 323 tonegative lished extending from positive battery at 326,

test jack 341, contact I cf switch element 304, front co-ntact of relaySIB, contact I ci switch element 306, contact I of lswitch element 301',front Contact of relay 3I8, Contact I of switch element 300, resistance339 to ground at 300. This produces a test circuit, enabling `thetesting'and `adjustment ofthe'separate contacts of the two repeaterrelays, similar to that described in connection with Fig. l'1. d

In Fig. 3, a motor control circuit for controlling the motor at station-330 from the main oilice station 30| shown. This motor control circuitis established by turning three-position switch 346 to its number threeposition.` The removal of switch Yelement 32| from the number onecontact, removes a short circuit which pre- *viously existedaround polarrelay 348, and connects this polarrelay effectively in series between'zoy windings 351 and 323 of relay 3|8. When the circuit is idle, theplug is removed from the jack at the nia-in oiice and negative currentsupplied from the main oice switchboard, through the winding of relay36|, inner contact of the jack, over the line 303 serves to maintainpolar relay 34S operated, thus closing the contact 350.

A circuit extending from ground through conductor 353, the' winding ofswitch relay 334, conductor 354, contact 3 of switch element 322,contact 2 of switch element 3M), conductor 355, contact 350, resistance324, to negative current supply at 326 serves to energize relay 334 thusclosing its front contacts 335, 336 and 331. From the repeater a circuitto station 330 may be traced, from negative battery at 326, throughresistance 324, front contact of relay 334, contact arm 335, winding 333of relay 3|6, through the circuit previously traced to line 33|, throughpolarized relay 363, motor control relay 365, front contact of relay 363to ground. Relay 365 being energized operates to hold the motor circuitopen.

In order to establish communication by calling from station 330, breakkey 366 is operated, thus breaking the line circuit and closing itagain. This will release and re-operate relay @E6 but relay 3|0 andpolar relay 348 will remain energia-ed. The contacts of relay 3i@ willopen and close again releasing relay 36| at the main office switchboard,and lighting the lamp 362. When released a contact of relay 36| shortcircuits its operating winding, so that relay 36| remains released afterthe line closes. When the cord associated with printer at the main oiceis plugged in to the line jack, positive current is supplied to line 303and relay 348 will be released, also releasing switch relay Insertion ofthe plug into the jack closes a circuit through a separate Winding onrelay 36|, restoring its contacts to normal and also completes a circuitthrough control relay 336, applying positive battery to printer 30|.Release of switch relay 334 connects positive battery to line 33| from326 through resistance 333, back contact of 335, the winding of relay3|6, back through the repeater to line 33| as previously traced, andalso connects the positive battery to the locking relay circuit of relay3 I8 from terminal 326, through the back contact of 331, contact 3 ofswitch element 3|9, back contact of relay 3|6, contact 2 of switchelement 335 to the relay winding of 3H through polar winding of 348,winding 323, as previously traced. This positive current on line 33|operates through the polar relay 333 to release the contacts 364, shortcircuiting motor relay 365, and closing the motor circuit to start theprinter motor. A more complete description of the motor operatingarrangement may he found in Patent No. 1,773,952, of, A. F. Connery,issued August 26, 1930.

Relays 348 and 334 remain released while the printer signals are beingtransmitted through the repeater in either direction. The operation ofthe repeater in repeating these printer signals is the same aspreviously described. A resistance 366 is shunted across the winding ofrelay 3|8 from ground at 340, through resistance 366, contact 3 ofswitch element 32| to the upper terminal of Winding 323, to reduce theinductive discharge from this relay winding when the circuit is openedat the main oice 36|. Without this shunt circuit the discharge may besuiicient to operate polar relay 348 during the transmission of thesignals. When the communication is completed, the plug may be removed atstation 30|,

reconnecting negative battery from 302 to the line, thus stopping thestation motor by the operation of polar relay 363 and restoring the lineto normal.

Although the motor control circuit has been described with a source ofboth negative and positive direct current supplied at the repeater asingle repeater may be installed with a single rectier or motorgenerator arranged to supply both current polarities at the repeater byreversal of the rectier or generator. In such a case the rectier orgenerator should not be grounded but both terminals should be connectedto the repeater terminals at 326 in Fig. 3. Terminal 351 should then beconnected to ground. The connection between ground and Wire 353 shouldbe removed and a connection made from 353 to terminal 369. Then wheneither terminal of the rectifier or generator is connected throughcontact spring 335 of relay 334 of the repeater to the station line, theother terminal will be grounded through spring 336 of switching relay334.

It is sometimes desired to provide a calling system to be operated fromthe main station for calling several subscribers printer sets so thatthe desired called station may be connected to the line. In accordancewith my invention such a system is indicated generally at 40|, connectedthrough push button switch or break key 402, line 463, polar relay 404at printer set 405, line 406,.,

repeater 401, line 409, polar relay 408, station printer set 4|0, and asuitable resistance 4| to a negative battery at 4|2.

The repeater station indicated at 401 in Fig. 4 may be a repeater suchas that illustrated in Fig. 3, with the switch 346 to the left or No. 3position or with switch 346 moved to its central or number 2 position.If the line sections are short enough so that they may be operated toground at one end,that if the first line section may be operated frombattery at the main omce to ground at the repeater, and the secondsection operated from battery at the repeater to ground at the terminalstation, then the repeater of Fig. 3 may be used with switch 340 in theNo. 3 position, as described above, and the polar signals transmittedover the line used to operate call bells or other signal apparatus toindicate the desired station to be connected. With this arrangement aprinter circuit such as shown in Fig. 4 is used. The break-key 402 atstation 40| may be operated successively to transmit the code signalsindicative of the desired station, and the relay 365 may be arranged tooperate a bell instead of closing the motor circuit.

However, the operation of the circuit of Fig. 4 with switch 346 in theNo. 2 position is more useful in cases where the lines are long.Negative battery is connected to line 406 from negative terminal at 326through resistance 31|, contact 2 of switch element 320, winding 323 ofrelay 3|8, winding of polar relay 348, winding 3|1 of relay 3|8, throughthe circuit previously traced to terminal 364 and to line 406. Theresistance 31| and grounded resistance 343 which is connected to relay3|8 through contact 2 of switch element 320 form a potentiometer, 'whichoperate to reduce the negative voltage supplied, below that of thenegative battery 436 at the main oice.

In the normal condition current from positive battery is connected tothe line at station 40| and flows through relay 348 in a direction tonormally maintain its contact 350 open. Interrupting this circuit tocall the main station 40| or to transmit printer signals will have noeffect, since the relay mally energized relay operatively connected inLb iasing spring'tends to hold the relay contact 350 open. When vthe pushbutton 402 at the main vo mce isoperated a reverse current is impressedon theline from negative battery 430, which current has a reducedstrength due to the negative supply which is impressed on the line atthe repeater. This reduced current is sucient to operate relay 404 orany other polar relays between themain central station and the relaystation, operating the call bell at any of these stations.

` Relay 3l8 will release as this weak currentin its upper winding 3l1opposes the current through its lower winding 323 and resistance 343,but the reversed current through the line will simultaneously operaterelay 348 closing contact 350. Opening of the front contact of relay 3l8will break the positive line supply on line 409 which formerly wassupplied from the positive terminal of. 326 and will impress on the linenegative polarity from the negative terminal of 326 through resistance324, contact 350, conductor 355, contact 2 of switch element 3l0,contact 2 of switch element 322 to terminal 332.

This will impress a negative current on line 409 operating. the Apolarrelays 408 and ringing the Abell at station 410, and any other stationswhich may be interposed in the line. When the pushrbutton 402 isreleased at the main oilce, positive battery is again connected to theline releasing relay 348 and reoperating the repeater re'- lay 318.These operations may be repeated every timev the push button isdepressed, thus ringing the 4bell as many times as desired. Any stationmay be called by assigning a particular number or code of thecall bellsthereto so that when the proper signal is received the printer at thatstation may be connected to the line.

Instead of repeating the current reversal to operate signal bells atother stations, it may be desired in some cases to use the single strokebell to vcall the. repeater station only. This may be 'done by openingline 355, Fig. 3, and connect- .ing a signal bell from the part ofconductor 355 connected with contact 350 to ground through a suitableresistance. Relay 348 will then respond to current reversal in the mainline, but will operate the local .signal bell instead of repeating thereversals over the other line.

vthe line relays 3I6 and 3l8 will operate only to transmit signalsthrough the test circuit and will not in any way affect the transfer ofsignals between stations on each of the now separate line sections.

While I have described my invention with relation to several specificembodiments thereof, it should be understood that these illustrationsare merely intended to describe the principles of operation of myinvention and not as a definition of the scope thereof. Any changes andsubstitution of parts may be made therein within the scope of theappended claims which thereto define Amy invention.

What is claimed is: 1. A repeater system comprising, a. i'irsttransmission line, a second transmission line, a nor.

each transmission line, contact means in each line controlled by therelay in the other line, each of said relays being responsive to signalcurrent iiuctuations in the transmission line associated therewith toopen and close contacts of said con-` tact means in said other line forrepeating sighals thereto, means operative .upon opening of saidcontacts in either of said lines for maintaining the relay-inthe openedlineenergized during 'the signal current fluctuations, and switchingmeans for disconnecting said contact means from both of said lines andcompleting the energizing circuit of said relays independent of saidcontacts for stopping the repeating of said signals from lone line tothe other, said switching. means establishing a local lcircuit throughboth of said contact means upon disconnection of' said contact meansfrom said lines.

2. A repeater system -according to claim l, in,

which said means for maintaining said relays energized comp-rises alocal circuit connected to a winding on each of said line relays, andsaid contact means in each of said lines comprises a' pair ofmake-before-break contact switches, one ofthe switches of each saidpairbeing connected l 3. A repeatervsystem according to claim 1, in

which said means for maintaining lsaid relays energized comprises alocal circuit connected to a separate winding on each of said linerelays, and further comprising a sounder circuit connected in shunt witheach of said separate windings and means for operating said sounder uponoperation of said repeating contacts.

4. A repeater system according to claim 1, in which said meansoperativeupon opening of the contacts for maintaining the relays in the linesenergized,v comprises a local energizing circuit connected to the mainrelay. winding of saidrelays.

5. A telegraph' system comprising a main ofce telegraph signallingstation connected to a first line section, a repeater connected to said-rst line section for repeating signal impulses and telegraph`signalling stations connected to the output of said repeater through asecond line section, means at said main ofce for supplying a normalpotential to said first line section, a polar neutral line relay in saidfirst line section at said repeater normally energizedrby said normalpotential supply, a polar relay in said rst line section at saidrepeater normally unoperated by said normal potential supply, means insaid second line section at said repeater responsive to signal impulsesfor repeating signals from saidA first line section to said second linesection, polar relays in said second line section at each of saidtelegraph stations, unresponsive to normal repeated signal impulses,means for maintaining a normal potential on said second line` section,means at said main office station for'introducing a current-of polarityopposite to said normal polarity upon said rst line section for operating said first named polar relay, means in said second line sectionresponsive to operation of said iirst named polar relay for introducinga current of polarity oppositeI to said normally maintained potential onsaid second line section for energizing said other polar relays, andoperating means at said telegraph stations responsive to energization ofsaid pola'r relays.

6. A telegraph system accordingl to claim 5 in 'in the transmission lineand the other switch of which said polar relays in said second linesection control call signal indicating means.

'7. A telegraph repeater comprising a rst line section, contact means insaid line section, a Iirst polar neutral line relay responsive to normalmake and break line signals, line signals, having a line windingconnected to said rst line section, a polar relay, responsive to polarcall signals, having a winding connected to said rst line section, asecond line section, contacts means in said second line sectioncontrolled by said first polar neutral line relay to repeat said makeand break line signals, a second line relay responsive to normal linesignals, having a line Winding connected to said second line section,said second line relay controlling repeater contacts in said first linesection, and a local circuit controlled by said polar relay operative tosupply potential of the polarity of said polar signals to said second`line section, whereby said repeater operates to repeat signals by theoperation of said line relays and to translate polar signals by theoperation of said polar relay.

8. A telegraph repeater according to claim 7, further comprising backcontacts operative with said contactmeans in said rst and second linesections, and another local circuit connecting line relays and said backcontacts for maintaining sai-d line relays operated upon the opening ofthe contacts in the line section connected thereto.

9. A telegraph repeater according to claim 7, in which said localcircuit is connected to said second line section, whereby said polarcall signals serve to repeat said call signals to said second linesection.

'10.A telegraph repeater according to claim 7, further comprisingswitching means for disconnecting said line contact means from theirrespective line sections, and completing another local circuit throughsaid contacts responsive to signals on said line section.

l1. A telegraph repeater according to claim '7, further comprisingswitching means for rendering said polar relay effective or ineffectivefor operation by polar signals incoming over said first line section.

12. A telegraph repeater system comprising a first line section, a linerelay in said rst line section, a second line section, a line relay insaid second line section, front contact means in each of said linesections controlled by the relays in the other line section, backcontact means controlled by said line relays for closing a holdingcircuit for the corresponding line relay upon opening of said frontcontact, a polar relay connected to said rst line section, and switchingmeans movable to alternative switching positions, for rendering saidpolar relay ineffective in one position, connecting said polar relay tocontrol a call signal indicator in a second position, and connectingsaidpolar relay to control telegraph motors in a third position.

13. A telegraph repeater according to claim l2, further comprising alocal test circuit and a cut switching means adjustable to twopositions, said out switching means in one position connecting saidfront Contact means in said line sections and in the other positiondisconnecting said front contacts from said line sections and closingsaid local test circuit through said front contacts.

GILBERT S. VERNAM.

